The invention relates to a device for fastening a cathode ray tube on a covering frame, in the case of which a flat flange which is fastened on the cathode ray tube and is provided with a bore is screwed to the covering frame by a screw, via an internal thread, there being arranged between the covering frame and flange a compensating element which, in a position which is determined by the cathode ray tube butting against the covering frame, can be fixed in relation to the covering frame in that the compensating element interacts with an internal-thread-containing guide part of the covering frame.
Such a device is known from European Patent 302026 B1. This device is intended to achieve two things. On the one hand, the intention is to prevent the guide part and the compensating element from rotating relative to one another in order to ensure that the screw is tightened, this being achieved in that the compensating element is divided up into a multiplicity of shaped sectors, of which each is introduced into a corresponding cavity in the guide part. As the figures of the European patent show, this results in a complicated design with the individual parts having a multiplicity of interengaging branches. On the other hand, the intention is to prevent the situation where, when the screw is placed in position, it cannot initially press onto the compensating element since in this case the compensating element, of which the position assumed under the stressing of the spring element between the covering frame and flange is responsible for securing the cathode ray tube, with allowance being made for tolerances in the process, could be deliberately forced out of position. In the case of the subject matter of the European patent, however, this last requirement is only fulfilled when the screw is actually inserted centrally into the device rather than in a somewhat skewed manner, which can never be ruled out in the case of quick assembly.
The object of the invention is to provide a device of the type specified in the introduction in the case of which displacement of the compensating element during insertion of the screw is more or less ruled out and the device as a whole is of simplified design.
This problem is solved according to the invention in that, by virtue of the screw being screwed into the guide part, the compensating element, by virtue of the guide part being widened in the region of said compensating element, can be clamped firmly on the guide part in that the guide part is of tubular configuration with at least one longitudinal slit and is enclosed by the compensating part, against which the guide part presses, when the screw is screwed in, with the longitudinal slit or slits widening in the process.
In the case of this configuration, the compensating element is only influenced by the screw when the screw, as it is screwed into the guide part, widens the latter and thus clamps the compensating element firmly on the guide part. This avoids displacement of the compensating element when the screw is placed in position and screwed in since the compensating element is clamped firmly as the screw is screwed into the guide part. The introduction of the screw into the guide part thus immediately ensures firm clamping of the compensating element in its assumed position, which is determined by the respective position of the covering frame in relation to the flange. Full allowance is thus made for the tolerances determining this position here by way of the position assumed by the compensating element, and this position is also retained in a stable manner on account of the firmly clamped compensating element, with the result that the cathode ray tube is secured in a solid manner on its covering frame.
In order, for the operation of inserting a cathode ray tube into a covering frame, to provide the compensating element with the ability to move, while remaining in abutment against the flange, the compensating element is expediently assigned a spring element which presses the compensating element against the flange. If, during insertion of the cathode ray tube, a certain amount of tilting then initially occurs on individual fastening devices, and this tilting is then eliminated with the definitive insertion operation, the compensating element, under the action of the stressing of the spring element, can follow this movement and thus remains constantly in contact with the flange.
On the one hand, the internal thread in the guide part may expediently be produced by a self-tapping screw; on the other hand, however, it is also, of course, possible for the internal thread to be preformed with underdimensioning.
The widening of the guide part may be produced, on the one hand, by the thread of the screw or by a screw-shank part which is provided, with overdimensioning in relation to the guide part, as a constituent part of the screw.
A particularly straightforward design is achieved in that the guide part has an inner tube and an outer tube, coaxial with the inner tube, with an annular space which is located between the two tubes and is essentially filled by the likewise tubular compensating element.
In order to provide specific and additional securing for the axial positions of the inner tube or guide part and the compensating element relative to one another, passing through the longitudinal slit or slits are one or more respective protrusions which belong to the compensating elements and extend into the region of the internal thread and continue the latter. This means that the screw is retained not just by the inner tube (as a constituent part of the guide part) but also by the protrusions of the compensating element, with the result that those regions of the screw thread which are in connection with the inner tube and the protrusions ensure that these regions and thus the inner tube and protrusions are secured at a defined spacing given by the thread of the screw, irrespective of how far the screw is screwed in.
In order also for the compensating element to be provided with a certain amount of radial elasticity, the compensating element may expediently be provided with one or more longitudinal slits. This makes it possible for the compensating element, when the screw is screwed in, to expand radially together with the inner tube and to be supported against the outer tube and thus to be clamped in relation to the latter.
In order to intensify the clamping between the inner tube and compensating element and/or compensating element and outer tube, the inner tube is expediently configured such that it has radial noses which have an outwardly decreasing cross section and project into corresponding recesses in a compensating element. Correspondingly, it is then also possible for the compensating element to be provided with radial noses which have an outwardly decreasing cross section and project into corresponding recesses in the outer tube of the guide part. The noses are then expediently configured such that the noses of the inner tube and the noses of the compensating element are oriented essentially in the same radial direction.
The retaining forces between inner tube, compensating element and outer tube can be further intensified in that those surfaces of the inner tube and compensating element and also of the compensating element and outer tube which are in contact with one another have a surface structure which makes relative displacement more difficult. This surface structure may be provided by roughening or knurling or the like.